Hydration-induced deformation of lipid aggregates before and after polymerization

The dimensions of multibilayer stacks of lipids with terminal diene groups were studied before and after polymerization at variable hydration by means of X-ray diffraction, gravimetry, and infrared spectroscopy. The short-ran ge hydration force acting between the bilayers of lipids with phosphatidylc holine and -ethanolamine headgroups is not affected by Lipid polymerization . Consequently, contributions to the interbilayer repulsion which are cause d by the mobility of individual molecules are obviously negligible at dista nces of less than a few tenths of nanometers. The polymerized lamellae beco me essentially incompressible in the direction parallel to the membrane sur face owing to intermolecular covalent bonds. The infrared frequencies of th e methylene stretching bands of the lipids correlate linearly with the area per molecules within the membrane plane. Consequently, infrared spectrosco py in combination with the osmotic stress technique represents a convenient method to estimate lateral compressibility qualitatively. The terminal die ne groups of bis(tetradecadienoyl)phosphorylethanolamine give rise to a rel atively Strong component of the lateral pressure which tends to bend the Li pid monolayers into inverse structures such as the H-II phase.